1. Field of the Invention
This invention relates to a valve assembly for a fluid-containing tank and method of making same and in particular to such a butterfly valve assembly which is bottom operable and is particularly adapted to be used in such a tank of a railway tank car, or the like.
2. Description of Prior Art
It is known in the art to provide a valve assembly for a railway tank car which is operable from the bottom of such tank car and such valve assembly may be disposed within the tank car or below the bottom of such car.
However, the Association of American Railroads (AAR) and the Department of Transportation (DOT) have railway tank car regulations which requires that projections extending in excess of 1 inch below the bottom of the tank of such a car must be protected by a skid, or if such a projection is part of a valve assembly associated with the tank car it must be capable of being sheared away without affecting the integrity of such valve assembly. In instances where a skid is provided this skid must be in the form of a ramp having a longitudinal dimension along the bottom of the tank which is three times the dimension projecting downwardly from such bottom.
U.S. Pat. Nos. 4,016,907 and 4,394,002, and copending U.S. patent application Ser. No. 549,200, for example, now U.S. Pat. No. 4,542,763, issued 09/124/85 disclose bottom operable butterfly valves for railway tank cars which extend below the bottom of the tank car and require protection.
U.S. Pat. Nos. 4,212,447 and 4,318,531, for example, disclose bottom operable valves disposed within such a tank car but such valves are of comparatively complex construction.
In addition, copending U.S. patent application Ser. No. 459,462 now U.S. Pat. No. 4,518,149 issued 05/21/85, also discloses a valve assembly for such a tank car wherein the valve assembly is disposed within the tank car; and such application also discloses the use of a butterfly valve assembly.
However, each tank car valve assembly of the character mentioned which has been proposed heretofore and is operable from the bottom of such tank car is deficient in certain respects. In particular, such a valve assembly either requires protection by a skid of the character mentioned; is of comparatively complex and expensive construction, or does not provide complete drainage of its associated tank.